[5.1] Use UTF8 instance that doesn't emit BOM

[apoorvdeshmukh]

Description

Ports #3399 to release/5.1

Issues

#3397

Testing

Port contains the testcase to validate the fix

[Copilot]

Pull Request Overview

This PR ports a UTF-8 encoding fix from the main branch to release/5.1. The fix addresses an issue where UTF-8 encoding operations were including a Byte Order Mark (BOM) when they shouldn't, which could cause data corruption or incorrect encoding behavior in SQL Server bulk copy operations.

Key changes:

• Replaces direct use of Encoding.UTF8 with a custom UTF-8 encoder that doesn't emit BOM
• Adds comprehensive test coverage for UTF-8 bulk copy scenarios
• Updates both .NET Framework and .NET Core implementations consistently

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
TestBulkCopyWithUTF8.cs	New test file that validates UTF-8 bulk copy operations preserve byte sequences correctly
Microsoft.Data.SqlClient.ManualTesting.Tests.csproj	Adds the new test files to the project compilation
DataTestUtility.cs	Adds helper method for creating test tables with specific column definitions
netfx/src/Microsoft/Data/SqlClient/TdsParser.cs	Replaces UTF-8 encoding instances with BOM-less version in .NET Framework implementation
netcore/src/Microsoft/Data/SqlClient/TdsParser.cs	Replaces UTF-8 encoding instances with BOM-less version in .NET Core implementation

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 65.97%. Comparing base (ee2d196) to head (5fc499d).

Files with missing lines	Patch %	Lines
.../netcore/src/Microsoft/Data/SqlClient/TdsParser.cs	80.00%	1 Missing ⚠️
...nt/netfx/src/Microsoft/Data/SqlClient/TdsParser.cs	80.00%	1 Missing ⚠️

Additional details and impacted files

@@               Coverage Diff               @@
##           release/5.1    #3617      +/-   ##
===============================================
+ Coverage        65.77%   65.97%   +0.19%     
===============================================
  Files              293      293              
  Lines            61647    61649       +2     
===============================================
+ Hits             40547    40671     +124     
+ Misses           21100    20978     -122     

Flag	Coverage Δ
addons	0.00% <ø> (ø)
netcore	70.26% <80.00%> (+0.15%)	⬆️
netfx	64.09% <80.00%> (+0.18%)	⬆️

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[benrr101]

Afaik, this will need to have the branch merged into it to pick up CI changes once they go through.